1. Field
The embodiments discussed herein are directed to a method and a thermal annealing apparatus of manufacturing a semiconductor device.
2. Description of Related Art
Efforts have been made to develop ferroelectric random-access memories (FRAM) having improved device performance. The FRAM stores information at a ferroelectric capacitor by means of a polarization reversal of a ferroelectric material. The FRAM is a non-volatile memory that continuously stores information even when power is removed therefrom. The FRAM includes a ferroelectric capacitor that is composed of a ferroelectric film sandwiched between two electrodes.
Chiefly used as materials of the ferroelectric film forming the ferroelectric capacitor are ferroelectric oxides having perovskite crystalline structure, such as zirconate titanate Pb(Zr,Ti)O3 (hereinafter referred to as PZT). In a typical production process, the ferroelectric film is formed using mainly physical vapor deposition (PVD) such as sputtering, and then subjected to a thermal annealing process for crystallization. For such a thermal annealing process, a thermal annealing apparatus is used. The thermal annealing apparatus heats a surface of a semiconductor wafer for a short period of time and then cools the semiconductor wafer.
Such a thermal annealing apparatus uniformly heats a semiconductor wafer at any temperature in the thermal annealing process subsequent to the PVD performed on the ferroelectric film. For example, Japanese Laid-open Patent Publication No. 11-195614 discloses one thermal annealing apparatus. Japanese Laid-open Patent Publication No. 11-171548 discloses another thermal annealing apparatus that performs the thermal annealing process on a ferroelectric film in an oxygen gas atmosphere in a thermal annealing chamber that is vacuumed and then supplied with an oxygen gas.
In accordance with Japanese Laid-open Patent Publication No. 11-195614, the temperature distribution of a semiconductor wafer is strictly controlled. A tube is arranged to introduce a gas into a thermal annealing chamber, but no detection means for detecting an oxygen concentration within the thermal annealing chamber is not arranged. The concentration distribution of the oxygen gas within the thermal annealing chamber may not be controlled. In accordance with Japanese Laid-open Patent Publication No. 11-171548, a certain amount of oxygen gas is introduced to reach a constant oxygen concentration of an oxygen atmosphere within the thermal annealing chamber in the thermal annealing process, and then the oxygen gas is only evacuated. For this reason, there take place variations in the oxygen concentrations in the vicinities of an oxygen supply pipe and an oxygen discharge pipe if one oxygen concentration is compared with the other oxygen concentration. If variations take place in the oxygen concentration, localized variations also take place in the supply amount of oxygen to an entire semiconductor wafer when the ferroelectric film is crystallized. Orientation of the ferroelectric film subsequent to the thermal annealing process on the semiconductor wafer may also suffer from localized variations.